Comment 1 for bug 1394228

I think it'd be a good thing to change the tests in pipeline_base that test transformers to use polling tasks, not pipelines directly, so this issue would surface there.

As for the fix, I'm thinking it'd probably be about grouping pollster_matches by source and then encompassing all of the pollsters for the same source in the same publish context.

Looking forward to reviewing the patch Igor :-)